The eastern black crested gibbon (Nomascus nasutus), also known as the Cao-vit black crested gibbon or the Cao-vit crested gibbon, is a species of gibbon from southeast China and north Vietnam.
Since the 1960s there had been no confirmed sightings of the eastern black crested gibbon and it was thought to be possibly extinct. In 2002 a small population was rediscovered in the Trùng Khánh District, Cao Bằng Province, in northeast Vietnam. In 2005 it was estimated that this population included about 35-37 individuals, and about 10 remain just across border in Jingxi County, Guangxi, China. It was thought to be extinct in China before the species was re-discovered by members of Kadoorie Conservation China.
The eastern black crested gibbon is classified as a separate from other crested gibbons based on molecular data, fur colouration, and differences in vocal communication. Previously it has been considered conspecific with the Hainan black crested gibbon or as a subspecies of the black crested gibbon. Until the sequencing of the mitochondrial cytochrome b gene the Hainan black crested gibbon was thought to be Nomascus nasutus hainanus, a subspecies of eastern black crested gibbon. The researchers proposed that the genetic separation showed it was a distinct species.
^Chan BPL, Tan XF andTan WJ, 2008. Rediscovery of the Critically Endangered Eastern Black CrestedGibbon Nomascus nasutus (Hylobatidae)in China, with preliminary notes on population size, ecology and conservationstatus. Asian Primates Journal 1(1): 17-25. http://www.primate-sg.org/storage/PDF/APJ1.1.nasutus.pdf